This invention relates to a boring machine, and more particularly to a minute and deep bore-making boring machine suitable for making minute, deep bores in a printed wiring board.
First, a conventional minute and deep bore-making boring machine used to make a minute, deep bore in a printed wiring board will be described.
FIG. 1 is a partially sectioned view of an example of a conventional minute and deep bore-making boring machine, and FIG. 2 a sectional view of a principal portion of another example of a conventional machine of this kind.
The boring machine of FIG. 1 has a compressed air-driven type spindle supported on air bearings. Referring to FIG. 1, reference numeral 1 denotes a spindle holding a drill 3 and supported rotatably in a spindle housing, 4 a turbine constituting a driving means for rotating (60,000-80,000 r.p.m) the spindle 1, and 8a, 8b, 8c air bearings supporting the spindle 1. These parts constitute a boring unit 20. Reference numeral 5 denotes a spindle feed mechanism provided integrally with the spindle housing 2 and supporting the same so that the spindle housing can be moved up and down. This spindle feed mechanism 5 is provided with a feed motor 5a for moving the former up and down. Reference numeral 6 denotes a workpiece to be bored by the drill 3, the workpiece being fixed by a workpiece-clamping mechanism 7.
FIG. 2 shows a principal portion, i.e. a boring unit of another boring machine, which has a spindle 1A driven by a high-frequency motor and supported on air bearings 8a, 8b, 8c. The parts shown in FIG. 2 and designated by the same reference numerals as in FIG. 1 are identical with those of such reference numerals in FIG. 1. Reference numeral 9 denotes a stator of the high-frequency motor in the spindle housing 2A, and 10 a rotor fitted in the spindle 1A.
The conventional boring machine of the above-described construction is not provided with a means for detecting the thrust force applied to the drill 3 when boring the workpiece 6 with the drill 3. Consequently, even when the thrust force increases while forcing to such an extent that the workpiece 6 and drill 3 are affected adversely thereby, boring contiues. Thus, feed control is impossible in this boring machine.
Therefore, when the thrust force mentioned above increases excessively, chapping of the inner surface of the bore as well as cracks and large burrs at the outlet of the bore readily occur. Hence, a high quality bore cannot be made, and, moreover, there is the possibility that the drill 3 will be broken.
There are some examples of a conventional boring machine in which the drill is controlled in accordance with a signal detected continuously during boring and representative of the torque in the direction of rotation of the drill, such examples being disclosed in, for instance, Japanese Patent Laid-Open Nos. 50079/1976, 93484/1976, 3776/1977 and 23792/1977. In all of these boring machines, torque in the direction of rotation the drill is measured so as to detect the cutting force applied by the drill. Therefore, the construction of these boring machines is complicated, and the boring units thereof cannot possibly be applied to a boring machine like the boring machine of the present invention which can be operated at a high speed of 60,000-80,000 r.p.m.
The conventional minute and deep bore-making boring machine is provided with no suitable detecting means; incapable as mentioned previously of controlling the cutting operation which is important for a boring machine; incapable of making a high-quality bore easily; and would cause the breakage of the drill during a bore-making operation.